The overall objective of this project is to investigate various cardiac defibrillation waveforms with the aim of finding the optimal combination of magnitude, timing, and waveshape necessary to ensure successful defibrillation at lower shock intensities. Such a study will result in a smaller and lower cost defibrillation system. The goals set for the year beginning September 1974 were as follows: 1) To gather data concerning the effectiveness of defibrillation using multiple shocks of 60 Hz of various durations and spacing. Complete electrical information about the waveforms used will be recorded. 2) To begin phase two of the project which involves the reduction and analysis of the data obtained. The data analysis will be done employing a digital computer and will make comparison easy regarding energies used, peak currents, etc. of the various waveforms.